Re: [PATCH] xen: domain_update_node_affinity: Correct the ASSERT

[George Dunlap <george.dunlap@eu.citrix.com>]

On 08/01/2014 04:12 PM, Jan Beulich wrote:
>>>> On 01.08.14 at 16:52, <julien.grall@linaro.org> wrote:
>> --- a/xen/common/domain.c
>> +++ b/xen/common/domain.c
>> @@ -449,7 +449,7 @@ void domain_update_node_affinity(struct domain *d)
>>           }
>>           /* Filter out non-online cpus */
>>           cpumask_and(dom_cpumask, dom_cpumask, online);
>> -        ASSERT(!cpumask_empty(dom_cpumask));
>> +        ASSERT( !d->vcpu || !d->vcpu[0] || !cpumask_empty(dom_cpumask));
>>           /* And compute the intersection between hard, online and soft */
>>           cpumask_and(dom_cpumask_soft, dom_cpumask_soft, dom_cpumask);
>>
>
> Actually, with sched_move_domain() having
>
>      /* Do we have vcpus already? If not, no need to update node-affinity */
>      if ( d->vcpu )
>          domain_update_node_affinity(d);
>
> it should really just be _that_ if() condition to get extended, and the
> ASSERT() left alone altogether. Or, if any other path can be proven
> to possibly reach the function with no vCPU allocated (I just went
> through them and didn't spot any), then it should really be an early
> bail from the function rather than a pointlessly complicated ASSERT()
> expression. (And for the record, your expression has a coding style
> violation anyway in that it begins with a space.)

I think changing the if() was what Julien started with; but overall I 
think that it makes more sense to update the assumption of the code in 
question than to require all the callers to be careful not to trip over it.

Doing an early bail might make sense as well.

  -George